It used to be said of the former order Violales (in the Cronquist botanical system), which is now part of Malpighiales, that hardly any list of characters defined it. The same is clearly true of this more broadly delimited order under the Angiosperm Phylogeny Group II (APG II) botanical classification system (seeangiosperm). However, some characters are quite common: the leaves of Malpighiales are often toothed and stipulate, and their basic floral construction is that common to basal eudicots—with sepals, petals, and often 10 stamens all free, a nectary, and superior ovaries with three to five fused carpels. In addition, the seeds have usually at most little endosperm, and the seed coat has a fibrous layer.

Malpighiales is a member of the Rosids I group of the core eudicots, perhaps most closely related to Oxalidales. In the past the families of Malpighiales were placed in a variety of orders, and many other families now placed in other Rosid orders were once thought to be related to these families. Included here are Flacourtiaceae, although the family as such is no longer recognized. It has been broken up into several parts, with most of its genera reassigned to Salicaceae and Achariaceae. Malpighiales as a clade has quite strong molecular support and is morphologically fairly coherent, even if not very distinctive. The families are generally organized into nine main groups, with a large number of unassigned families, as listed here:

Malpighiaceae and Elatinaceae

Malpighiaceae contains 68 genera and 1,250 species of lianas to trees, which are found throughout the tropics, although especially in the Neotropics, and into the subtropics. Byrsonima (150 species), Malpighia (130 species), Heteropterys (120 species), Stigmaphyllon (100 species), Banisteriopsis (90 species), Bunchosia (55 species), Mascagnia (50 species), and Malpighia (40 species) are all restricted to the New World. Acridocarpus (30 species), mostly from Africa, is the largest genus in the Old World. Members of Malpighiaceae usually have opposite leaves that lack teeth. The hairs are single-celled and T-shaped, and there are often conspicuous glands on the leaf or petiole. The characteristic flowers have four or five sepals, often with large paired glands on their backs; the petals are strongly narrowed and stalked at the base and are crumpled in bud; and there are three carpels, each with a single ovule. There is no nectary, and pollination is effected by bees, which remove waxes from the sepal glands. The pollinating bees are absent in the Old World, and members of Malpighiaceae there may lack sepal glands or may secrete nectar. The sepals and filaments often persist at the base of the fruit, which is typically dry and with a variable number of wings.

Elatinaceae contains 2 genera and 35 species of herbs to subshrubs, which are native to moist or wet habitats worldwide, although most are tropical or subtropical. Bergia (25 species) and Elatine (10 species) are especially widespread genera. Members of Elatinaceae have opposite, more or less toothed leaves with small paired thin and brownish stipules. They have very small flowers. Elatinaceae species are often important economically as weeds in rice fields and irrigation ditches, where they also play an important ecological role in the prevention of soil erosion.

The Salicaceae group

Salicaceae, Violaceae, Achariaceae, Malesherbiaceae, Turneraceae, Passifloraceae, and Lacistemataceae form a related group. Glands on the leaves are common; there are often three carpels; ovules are borne on the walls of the ovary; and the reserve endosperm in the seeds is persistent and oily.

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